I have the same setup - SBC/Yahoo! DSL using the 4100 modem. I have not had to access the server or anything even remotely similar. I simply plug in the computer and go.

Your problem might be related to the software that SBC sends you with their modem. It appears to be designed to hamper users, instead of helping them. You might want to consider removing that software and simply using the modem as it is. I have done this with both Windows and Linux, with good results.